Motorcycles Have Gotten Lighter. Why Haven't Cars?

The Steering Column

October 2005 By CSABA CSERE

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Engineers who deal with vehicles are usually obsessed with weight. That's because whether a machine rolls on wheels, flies through the air, or floats in the water, every extra ounce makes it more difficult to accelerate, stop, or change direction. Extraneous ounces also require more energy to maintain any desired speed. That's why, whether the conveyance is an F-22 jet fighter, an America's Cup yacht, or a Formula 1 car, designers and engineers put enormous effort into reducing weight.

If less weight equals better performance, then why are cars getting steadily heavier—a lot heavier? When I've suggested to industry engineers that every modern car and truck should lose between 500 and 1000 pounds, I've heard no argument.

The usual excuse for this vehicular corpulence is increased customer demand for stiffness and rigidity. These expectations are compounded by modern tires, which are much wider and stickier than '70s rubber, and vastly more powerful modern engines. Both of these improvements tend to bend and twist vehicle structure to a greater degree, while the customers want their cars to feel more solid and stable. The engineers lament that the only solution is more heavy metal. But does it need to be this way?

Motorcycles have undergone a similar transformation in the past 25 years. But rather than pork up, they've become much lighter, as I was reminded recently during a day spent riding Yamaha YZF1000-R1 sport bikes at a track. Yamaha's PR man, Brad Bannister, knows that I own an R1, which is how I ended up trying to stay alive piloting one of the fastest motorcycles on the planet at the Willow Springs high-speed circuit.

With some 150 horsepower at its rear wheel, the latest brakes, and enough cornering clearance for a good rider—not me in my old leathers—to drag a knee, the R1 never twitched, wobbled, or slid during my 60-plus laps around the track. Even allowing for my doggy pace, this was a quantum leap over the bikes I road-raced in the '70s. Back then, even the best street bikes would scrape their foot pegs and exhaust systems in every curve, wiggle like a freshly hooked bass when accelerating out of a corner, and fade their brakes so badly that the front brake levers would touch the handlebars.

One of those older machines shares my garage with the R1. It's a 1979 Honda CBX powered by a six-cylinder engine that made it the fastest bike in its day. The evolution from this bike to my 2004 R1 includes the same increased need for chassis stiffness that cars experienced during the same period.

For example, the CBX wears a 3.50-19 front tire and a 4.25-18 rear tire, both on 2.15-inch-wide rims. The R1 uses a 120/70-17 front tire on a 3.5-inch rim and a 190/50-17 rear tire on a 6.0-inch-wide rim. Converting from inches to millimeters, that's a 35-percent-wider front tire and a 76-percent-wider rear tire on vastly wider rims. Combined with a switch from bias-ply to radial construction and the progress that's been made with rubber compounds, the R1 has enormously higher grip and cornering force than the CBX ever did.

Similar advances have occurred in the engine room. In contemporary tests, the '79 Honda's 1047cc transverse six—with four valves per cylinder, double overhead cams, and six carburetors—developed, at the rear wheel, 86 horsepower at 9000 rpm and 52 pound-feet of torque at 6500 rpm, with a redline of 9500 rpm. That was good for a quarter-mile of 11.4 seconds at 118 mph, according to our sister magazine Cycle World, and no other stock motorcycle could touch it.

My current-generation R1 has a 998cc four-cylinder engine with double overhead cams, five valves per cylinder, an engine-management system that employs fuel injection, and a big butterfly valve in the exhaust system to tailor engine breathing to changing rpm. At the rear wheel, Cycle World measured 152 horsepower at 12,750 rpm and 73 pound-feet of torque at 10,000 rpm. The redline is 13,750. In its testing, the bike scorched the quarter in 10.2 seconds at 141 mph.

Yet despite being pushed, pulled, and twisted by bigger, stickier tires, more powerful brakes, and 77 percent more power, the R1 weighs only three-quarters as much as the CBX—447 pounds for the new Yamaha versus 596 pounds for the old Honda.

In the four-wheeled world during a similar time period, weight has moved in the opposite direction. A 1980 Porsche 911SC (172 horsepower, 225/50-16 rear tires on 7.0-inch wheels) weighed 2700 pounds. The latest 911 (321 horsepower, 265/40-18s on 10.0-inch wheels) weighs 3253 pounds. The 2850-pound 1979 Datsun 280ZX has become the 3360-pound Nissan 350Z. Mazda's '79 RX-7 weighed a feathery 2340 pounds. The current RX-8—which is light for '05—still weighs 600 more pounds.

So why have bikes slimmed down while cars have swollen? The difference is materials and structural design. The CBX frame is simply a collection of welded steel tubes. The R1 uses large-section cast-aluminum beams that are stiffer and lighter. The CBX has a chrome-plated-steel exhaust system. The R1 uses titanium everywhere, except for the catalyst—yes, this more than 150-hp-per-liter engine has emissions controls. Throughout the bike, where the CBX has steel, the R1 uses aluminum or plastic.

Meanwhile, cars are still built pretty much the same as they've been for a half-century, made from spot-welded steel stampings. Some of the steel is a little stronger and the parts are more optimized using computer-aided modeling, but the technique remains largely unchanged.

The handful of cars that haven't gained much weight over the past quarter-century have broken with this traditional construction. The Ferrari 360 Modena has adopted an aluminum structure. The Chevrolet Corvette also uses a lot of aluminum as well as magnesium and composite materials in an innovative structure.

Until other cars and trucks take advantage of the latest materials and more imaginative construction techniques, they will continue to pork out.